Devices (hereinafter referred to as “MEMS variable capacitance devices”) in which MEMS are applied to variable capacitance elements can achieve low loss, high isolation and high linearity, and therefore are expected as key devices for achieving multiband and multimode portable terminals as the next generation portable terminals.
When applied to a wireless system based on GSM (global system for mobile communications) standards, a MEMS variable capacitance device is required to perform switching in a state in which radio frequency (RF) power of the order of 35 dBm is applied. That is, with the RF power of the order of 35 dBm being applied, a movable upper capacitance electrode included in the MEMS variable capacitance device needs to be returned from a state (down-state) in which the upper capacitance electrode is lowered toward a lower capacitance electrode side to a state (up-state) in which the upper capacitance electrode is pulled upward from the lower capacitance electrode side. Such switching operation when RF power is applied is referred to as “hot switching”.
One method for achieving hot switching is to increase the spring constant of a spring structure (or a support member) connected to an upper capacitance electrode. However, if the spring constant of the spring structure is increased, the operation of pulling up the upper capacitance electrode from the lower capacitance electrode side becomes easier, whereas a large driving force (e.g., electrostatic attraction) becomes necessary for the operation of pulling down the upper capacitance electrode toward the lower capacitance electrode side.
To obtain a large driving force, a driving voltage for driving the MEMS variable capacitance device needs to be increased, or the area of a driving electrode needs to be increased.
In the case of increasing a driving voltage to obtain a large driving force, there arise problems, such as the increased area of a boost circuit which boosts a potential supplied from the outside up to the driving voltage, the increased power consumption, and longer switching time.
In the case of increasing the area of a driving electrode to obtain a large driving force, the chip area is increased, which leads to increased manufacturing cost.